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mostly dried up, and the only remains of them now are a series of much smaller lakes, occupying hollows in the bottoms of the old lake basins. Great Salt Lake is the modern representative of Lake Bonneville; and Tahoe, Winnemucca, Pyramid and other lakes occupy the basin of Lake Lahontan.

The region about the manganese deposit is on the eastern edge of the area defined by Mr. Russell as the ancient bed of Lake Lahontan, and occupies a position at the head of what was once a small bay protruding about fifteen miles up what is now the valley of the Humboldt River. Mr. Russell,^[1] in speaking of the lakes which formerly existed in the Great Basin, says: "Some of these old lakes had outlets to the sea, and were the sources of considerable rivers, others discharged into sister lakes; a considerable number, however, did not rise high enough to find an outlet, but were entirely inclosed, as is the case with the Dead Sea, the Caspian, and many of the lakes of the Far West at the present time." Lake Lahontan did not overflow, and, therefore, the mineral matter brought to it in solution by tributary waters constantly increased in quantity; while the gradual evaporation of the lake steadily concentrated these mineral solutions until they arrived at a state of supersaturation, and were deposited as chemical precipitates. These were, according to Mr. Russell, largely of a calcareous nature, and were laid down as fringes on the margin of the lake at successive stages of evaporation. They are found now at different levels on the old lake border, and mark the ancient shore lines. Mr. Russell has divided them into three classes of "tufas," differing considerably in physical character, and deposited at different levels during the desiccation of the lake. He has named them in the order of their chronological succession, "lithoid," "thinolitic," and "dendritic" tufas. From the analogy of the samples of tufa collected by the writer at the manganese deposit with the description of lithoid tufa given by Mr. Russell, and from the position that the deposit occupies in the old Lake Basin, it is probable that